1. Field of the Invention
The present invention relates to a subframe structure of a vehicle.
2. Description of the Related Art
A subframe is provided below a side frame on a front side portion of a vehicle body. A steering gear box or a vehicle drive unit such as an engine may be mounted on the subframe, and the subframe supports a suspension.
In order to absorb an impact of a collision on a front side of the vehicle, there has been proposed a technique in which the subframe is downwardly bent at the time of collision. For example, Japanese Patent No. 3,188,946 discloses a forwardly ascending slope portion formed at a front part of a subframe, and a steering gear attached to the slope portion. In this configuration, when a head-on collision occurs, the slope portion of the subframe is moved to become close to vertical, whereby the steering gear attached to the slope portion is suitably moved downward.
According to a technique disclosed in Japanese Patent No. 3578087, when a collision load is input to a subframe by a forward-backward collision of a vehicle, the subframe is bent and deformed in a V shape around a middle portion thereof, whereby a power unit moves downwardly with respect to a vehicle body. In addition, a mounting chamber is connected to an upper portion of the power unit with a rod. Thus, the collision load is input to the upper portion of the power unit, whereby the power unit is rotated around a lower portion connecting point in a front-and-rear direction. Consequently, the shortest distance between the power unit and a partition wall increases as compared with a state before the collision. Therefore, a crushing stroke in the front-and-rear direction can be increased without increasing the entire length of the mounting chamber.
According to the disclosures of Japanese Patent No. 3188946 and Japanese Patent No. 3578087, the subframe is fixed to a lower surface of a side frame with a bolt. In this case, a collision load input to a bumper beam is transmitted to the subframe through the side frame. Also, there is a fear that a slip may occur between attaching surfaces of the side frame and the subframe. Therefore, it is difficult to efficiently transmit the load to the subframe. Accordingly, there is a problem that it is difficult to control a crushing mode of the subframe at the time of collision of a vehicle.